The Collaborative Ocular Melanoma Study is a multicenter, randomized, controlled clinical trial designed to compare the efficacy of enucleation versus irradiation in the treatment of eyes with choroidal malignant melanomas. Candidates for the study will be newly diagnosed cases with unilateral choroidal melanomas measuring between 3 mm and 8 mm in height and up to 16 mm in basal diameter, with no evidence of metastatic disease, and in patients 21 years of age or older. Informed consent will be obtained from all patients prior to randomization. The outcome of primary interest is death from all causes. Secondary outcomes will include death from cancer, whether metastatic or not, diagnosis of other tumors, and preservation of vision. Complications of irradiation and changes in visual acuity will be documented and carefully monitored throughout follow-up. Standardized clinical and data collection procedures will be employed, and standardized forms will be used in all centers. Central training and certification of all study staff will be required. Tumors larger than 8 mm in height or 16 mm in diameter will be entered into a separate substudy, comparing enucleation preceded by preoperative external irradiation versus enucleation alone. The study will be conducted in cooperating clinics located throughout the United States. It will be directed by an Executive Committee consisting of 12 to 15 study investigators and a Steering Committee to deal with day-to-day operational decisions. An independent Data and Safety Monitoring Committee will be responsible for assuring ethical conduct of the study and for reviewing the accumulating data on a regular basis for evidence of adverse or beneficial effects of therapy.